Dynamics of vortex nucleation in nanomagnets with broken symmetry

We investigate the dynamics of magnetic vortex nucleation in sub-100-nm mesoscopic magnets with the aim of establishing an independent control of vortex polarity and chirality. We consider the dynamic behavior of the vortex spin structure in an object with broken symmetry-a Pacman-like nanomagnet shape-proposing a model based on classical electrodynamics and providing a proof by conducting micromagnetic calculations. The model provides evidence that the desired vortex chirality and polarity could be established by applying solely quasistatic in-plane magnetic field along specific directions with respect to the structure's asymmetry. We identify the modes of vortex nucleation that are robust against external magnetic field noise. These vortex nucleation modes are common among a wide range of sub-100-nm magnets with broken rotational symmetry. The results could lead to the practical realization of high density magnetic memories based on magnetic vortices.